With the rapid development of electronics technology, various electronic products have become a necessity in people's lives. The power supply is one of the components of the electronic equipment. The DC-DC converter is an important part of the switching power supply. The power consumption of the converter is one of the important indicators to measure the performance of the power supply. When the power tube of the switching power supply is turned on at different times of the switching cycle, the switching loss of the switching power supply is different. The switching loss is minimized when the power tube is turned on at the lowest drain voltage.
In Buck topology, when the power tube is turned off and the current of the inductor L drops to zero, LC resonance occurs in the inductor L and the parasitic capacitance Cp at the drain terminal of the switch transistor. Similarly, when the power tube is turned on at different times of the resonance, the switching loss of the converter is different. Wherein, when the resonance at the drain terminal of the power tube reaches the valley point, the drain voltage of the power tube is the lowest, and the switching power loss of the power tube is minimized. In the conventional control method, the valley signal Valley and the enable signal C of the gate driving circuit are the same signal. There is a certain delay from the generation of the enable signal C of the gate driving circuit to the actual conduction of the power tube, so that the power tube is turned on after the valley point, resulting in high system power consumption. Additionally, the external LC resonant frequency will vary with application conditions, and the delay of gate driving circuit will also be affected by changes of other factors, for example, the type of external power tube and temperature, etc. Therefore, the conventional method will make the system consume different amount of power in different applications, which cannot be widely used.